Abstract Background: KRAS-driven cancer represents ∼25% of cancers, with high rates in pancreatic cancer (PDAC), colorectal cancer (CRC), and non-small cell lung cancer (NSCLC). Mutated KRAS and TGF-β signaling activate cancer-associated fibroblasts (CAFs), creating a fibrotic extracellular matrix (ECM). The fibrotic ECM promotes immunosuppression and tumor growth but is potentially reversible with KRAS inhibitors (KRASi). We have recently demonstrated that myofibroblast CAFs (myCAFs) in KRAS-mutated PDAC express high levels of collagens III, V, VIII, XI, and XII. In this study, we investigated the landscape of KRAS-induced myCAF activation and ECM change across KRAS-mutated cancers. We utilized these changes to identify biomarkers for KRASi efficacy. Methods: Patients with KRAS-mutated PDAC (n=141), CRC (n=223), or NSCLC (n=74) were evaluated for collagen expression and gene-set variation analysis (GSVA) was used for hallmark KRAS and TGF-β signaling. Correlations of KRAS and TGF-β signaling, and collagen expressions across cancers, were evaluated using Spearman correlation. Single-cell RNA-seq data from KRASi treated KPPC mice was analyzed using Seurat. CAFs were subclustered and subtypes identified from marker genes (myCAF, inflammatory CAF, and antigen-presenting CAF). CAF subtype and collagen expression were compared between KRASi and vehicle with Fisher’s exact test and Wilcoxon rank-sum test, respectively. Biomarkers for formation of collagens I (PRO-C1), III (PRO-C3), V (PRO-C5), VIII (PRO-C8), XI (PRO-C11), and XII (PRO-C12) were measured in serum from healthy controls and patients with PDAC, CRC, or NSCLC. Differences between cancer and control were evaluated by Wilcoxon rank-sum test. Results: KRAS signaling was significantly correlated with TGF-β signaling and expression of COL3A1, COL5A2, and COL8A1 across patients with KRAS-mutated PDAC, CRC, and NSCLC (R0.4, p0.05). Significantly increased expression of Col3a1, Col5a2, Col8a1, Col11a1, and Col12a1 was observed from fibroblasts in KRASi treated PDAC compared to vehicle (p0.001). Significantly fewer myCAFs in KRASi treated PDAC (p0.001) suggested reduced myCAF-derived ECM with KRAS inhibition. Serum biomarkers for formation of myCAF collagens (PRO-C3, PRO-C5, PRO-C8, PRO-C11, and PRO-C12) were significantly upregulated in patients with PDAC, CRC, and NSCLC compared to healthy controls (p0.001). Type I collagen formation was unaffected (PRO-C1, p=0.37), suggesting KRAS-specific collagen formation. Conclusion: KRAS-mutated tumors have a myCAF-enriched microenvironment with a unique collagen expression profile that is altered by KRAS inhibition. Non-invasive myCAF-derived collagen biomarkers that are elevated in serum from patients with KRAS-driven cancers, can potentially quantify KRAS signaling and track KRASi efficacy to guide clinical decision-making. Citation Format: Martin Birkmose Rasmussen, Rasmus Sund Pedersen, Nicholas Willumsen, Morten Karsdal. The myCAF and ECM landscape in KRAS-mutated cancer: Utilizing liquid biomarkers to track KRAS-induced fibrosis and KRAS inhibitor efficacy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2441.
Rasmussen et al. (Fri,) studied this question.